1. Field of the Invention
The invention relates to the field of data communications, and more particularly to a system for communicating utility meter readings over two or three wire lines.
2. Description of the Prior Art
Utility data communication systems are used to transmit consumption data from a meter, such as an electric, gas, or water meter, to remote meter reading units. In these types of systems, each meter includes an encoder which converts consumption information displayed by a mechanical or electronic register associated with the meter to a form which can be transmitted over wires or the like to a remotely located meter reading unit. One such encoder for use with meter registers is shown in U.S. Pat. No. 4,085,287. As shown in this patent, a series of conductive pads and a movable contact are associated with one or more odometer-type register display wheels. The position of the movable contact with respect to the conductive pads indicates the register wheel position and hence the quantity being displayed by the meter register. Upon interrogation by a remote meter reading unit, the register position information is transmitted via three conductive wires to the remote meter reading unit. Data is transmitted from the encoder to the remote reader.
As set forth in U.S. Pat. No. 4,085,287, the remote unit may be portable and include a plug for insertion into a receptacle connected to the three wire data line. A meter reader thus can carry the portable meter reading unit and, by plugging it into the appropriate receptacle remotely read an individual meter register.
It is also known to connect encoded meter registers of the type shown in U.S. Pat. No. 4,085,287 to a device commonly known as a meter interface unit or MIU. Such an arrangement is shown in U.S. Pat. No. 4,852,152. In this arrangement, each encoded register is permanently connected to an MIU. In turn, the MIU contains an interface allowing it to respond to interrogation signals applied over a telephone line. A utility may call the MIU, via special telephone central office equipment, to "wake it up". The MIU then interrogates one or more encoded registers connected to it and sends the meter reading data over the telephone line back to the utility.
An alternative to the three wire encoded utility meter data transmission system shown in U.S. Pat. No. 4,085,287, is a two-wire, inductively coupled utility meter data communication system such as shown in U.S. Pat. Nos. 4,782,341, 4,758,836, 4,652,877 and 4,463,354. In this type of system, a portable meter reading unit is provided with an inductive loop or coil which mates with a similar loop or coil arranged on a receptacle. The coil of the receptacle is coupled via two lines to a meter register. The coil of the reading unit is brought into proximity with the coil of the receptacle and an AG interrogation signal is applied to the coil connected to the meter. This AC signal is transmitted to the remote meter register by means of the mutual inductive coupling of the two coils. This interrogation signal to used to "wake up" the encoded meter register which then sends back the meter reading data by modulating an AC carrier signal. The AC carrier signal can be generated internally by the meter encoder or may be the AC interrogation signal itself.
While the above meter reading systems have gained wide acceptance, they are subject to several drawbacks and limitations. While the inductively coupled two-wire meter reading systems described above allow data communications to take place between an encoded meter register and a portable meter reading unit, this arrangement is unsuitable for use with conventional meter interface units which require direct, three-wire connection to an encoded meter register for data communications. In addition, both the two-wire and three-wire meter reading systems using portable reading units require the use of a separate wired receptacle for each encoded meter register which is to be read. This presents an inconvenience to the meter reader especially in situations where there are a large number of encoded meters to be read within a small geographical area. This can occur in office buildings and high density housing (e.g. apartments, condominiums, townhouses, etc.) where each unit is individually metered. The meter reader in such a situation would be faced with the time consuming task of having to plug and unplug his portable meter reading unit tens and possibly hundreds of times in order to individually read each of the encoded meters. The use of a separate receptacle for each encoded meter obviously increases the cost of installation for the utility, also.
In addition each different utility (e.g. gas, water, and electric) has traditionally provided their own separate receptacles for reading of their respective meters. These utilities not infrequently utilize different data formats from each other making it infeasible for a single meter reader to read all the meters of different types of utilities.
It would therefore be of great benefit for utilities to have a data communication system for reading utility meters which could be used in both two-wire inductive coupling and three-wire metallic coupling modes and which is also adaptable for connection to an MIU for the purpose of central meter reading. It would also be of great benefit to have a meter reading system where multiple remote meter registers could be linked together over a single set of lines to a single receptacle to enable all these meters to be read by a portable meter reading unit without the need for separate receptacles and connections to each one. Furthermore, it would be of great benefit if the meter reading unit or MIU were able to automatically recognize and read different types of meters and meters of different manufacturers.